1. Field of the Invention
This invention relates to a covergence circuit board for a color cathode ray tube and in particular to a device for mounting the covergence circuit board as an integral part of the color cathode ray tube.
2. Description of the Prior Art
Color television receivers typically use a three-beam shadow mask type of color cathode ray tube (CRT) by which to converge the electron beams at all points of the viewing screen scanned by the beams. Such apparatus usually consists of a device or devices for effecting static convergece of the beams at some reference point such as at the center of the screen. Additionally, the covergence apparatus includes electromagnets by which to dynamically control the convergence of the electron beams over the entire screen. Such dynamic convergence apparatus is energized by waves varying as a function of the deflection angle of the electron beams.
It has been customary in most color CRT's to mount a convergence magnet structure at a suitable point along the neck of the CRT to influence the electron beams before they are deflected to scan the usual raster. The circuit by which the waves applied to the respective magnetic structures are suitably adjusted has, in most cases, been located on a separate control panel. The use of a separate control panel facilitates the convergence alignment in the color television receiver, which requires adjusting a large number of controls grouped together upon the control panel, typically in the form of a printed circuit board. Such a separate control panel typically would require a metal bracket, which in turn is secured by clips, bolts or other suitable fasteners to a part of the television receiver cabinet. In order to align the color convergence of the color CRT, the control panel is removed and placed in a position so that the TV technician may observe the front of the CRT screen while adjusting the controls on the convergence control panel. However, this requires a relatively long connecting cable between the convergence control panel and the convergence magnets disposed about the neck of the color CRT. In addition to a rather expensive mounting assembly upon the cabinet of the color receiver, the convergence control panel is not an integral part of the chassis or the picture tube, thus causing a potential problem during the manufacture and assembly of this receiver in that the convergence control panel must be specially handled during the movement of the receiver from work station to work station in order that it might not be damaged.
Further, the mounting of the convergence magnets associated with the convergence control panel should be of such a character that the coil elements of these magnets are urged into firm contact with the glass envelope of the color CRT to minimize the non-magnetic gaps between the coil elements and the cooperating pole pieces mounted internally of the CRT envelope.
In recent color CRT receivers, the convergence control panel has been mounted integrally about the neck of the color CRT, as shown in U.S. Pat. No. 3,377,515 of J. W. McLeod, Jr., and U.S. Pat. No. 3,818,395 of A. M. Anthony et al. In a further U.S. Pat. No. 3,637,930 of J. L. Meier, assigned to the assigned of this invention, there is shown an assembly for holding a number of circuit elements, not specifically designated to be the convergence control circuitry, that is disposed about the neck of the cathode ray tube. A particular problem associated with the mounting of such circuit boards about the neck of the color CRT resides in the adjustment of the circuitry and in particular the adjustment of the color convergence circuitry. In particular, the magnets associated with the color convergence circuitry must be very accurately placed with respect to the color electron guns of the color CRT in order to ensure accurate convergence. If during the adjustment process, the relative position of the printed circuit board and therefore the electromagnets disposed thereon is moved with respect to the color CRT electron guns, the convergence will be defeated. In addition, in order to view the front or screen of the color CRT while making adjustments of such convergence control boards, it is necessary to use a mirror, posing the additional problem of viewing a reversed image and further, with ordinary mirrors, the reflection of multiple images, making it difficult to observe the precise orientation of the series of lines or bars produced upon the display screen of the color CRT during convergence adjustment procedures.